The invention relates to a fluid friction clutch with a primary part which includes a driving disk and a secondary part which includes a housing. The primary and secondary parts are rotably supported for rotation with respect to one another and the driving disk is arranged to rotate in a working space in the housing. By means of an intermediate disk secured to the housing, the working space is separated from a fluid storage space formed in the housing. An inlet bore leads from the storage space to the working space and accommodates transfer of clutch fluid which serves as the drive transfer medium between the driving disk and the housing. The clutch fluid inlet opening is controlled by means of a valve lever, which is in turn controlled by an actuating member engageable with a bi-metallic temperature responsive strip for controlling the opening of this inlet bore. The bi-metallic strip is clamped under ribs provided at the front side of a housing cover and is prevented from relative rotational movement by means of tongues formed at the ends of the bi-metallic strip and at an angle to the plane of the bi-metallic strip.
By way of background information as to the type of clutch the invention relates to, see my commonly assigned U.S. Pat. No. 4,278,158.
In known fluid friction clutches of this kind, a valve lever is mounted at an intermediate disk in the clutch housing which separates the housing into a work space and a storage space. This valve lever serves for the control of the input of clutch fluid to the working space. A control rod or member at the center of the housing cover engages with the valve lever and is engageable with a bi-metallic strip at the outside of the housing cover. The temperature dependent bending of the bi-metallic strip is transferred by means of the control member to the valve lever, which valve lever in turn controls the opening and closing of a bore connecting the storage chamber with the work space, whereby the engagement of the clutch is controlled.
With this known construction, radially extending cooling ribs are arranged on the housing cover at the outer radial regions thereof, which cooling ribs are cut-away at their ends facing the middle point of the cover so as to form a stepped opening together with the cover. These cut-outs serve for the receipt of the ends of the bi-metallic strip which can be clamped between diametrically opposite ribs and thereby held in place over the control member which engages the middle of the bi-metallic strip.
An arrangement of the above-mentioned type has been contemplated wherein the shifting member has a predetermined pressure against the bi-metallic strip which is elastically clamped at its end regions at the underside of the ribs at a spacing from the housing cover. The attachment in the circumferential direction is provided to tongues bent into the end region of the bi-metallic strips, which tongues are engageable between two adjacent cooling ribs. With this type of arrangement for temperature responsive control, the bi-metallic strips must be exactly clamped in order to assure a certain clutch characteristic. Therefore with small variations in the position of the bi-metallic strip, a change in the clutch characteristic can result. It has been learned, that especially during servicing or repair work on the clutch, the position of the bi-metallic strip can change. For example, the position of the bi-metallic strip can be changed when the clutch is being removed, or also when unintentional disturbances occur, for example when a tool engages the bi-metallic strip.
The invention is based upon the problem to develop a fluid friction clutch which does not have its clutch characteristics changed during the repair or servicing, or unintentional disturbance of the bi-metallic strip.
The invention contemplates providing an elastic securing medium in the region of the clamping positions of the bi-metallic strip so as to fixedly attach the bi-metallic strip to the housing cover. With this arrangement the bi-metallic strip is held by means of an elastic clamping closure at the housing cover, which can absorb small movements of the bi-metallic strip, while always returning to its original position. After a successful exact assembly of the clutch, the bi-metallic strip cannot be removed from the cover without disturbance or destruction of the securing medium. In this way, an ever constant clutch characteristic is guaranteed. The securing mass also results in an advantageous vibration damper, by preventing engagement of metal on metal and thereby preventing deflection of the fastening position.
According to a particularly preferred embodiment of the invention, a silicone mass is provided as the elastic mass or plug, which silicone mass is injected into the region of the clampling position and is there hardened, so that it encompasses the ends of the bi-metallic strip and is partly disposed between the cooling ribs. The invention also contemplates the injection of a silicone mass on existing fluid friction clutches whereby the end regions of the bi-metallic strips are then elastically fixed to the housing cover.
In an especially advantageous embodiment, an opening is provided in the bi-metallic strip between the tongues at its ends. With this arrangement the clamping procedure for the bi-metallic strip can proceed as previously. However the elastic silicone mass can be better supplied through this opening after the clamping, especially in the region between the housing cover plane and the underside of the bi-metallic strip so that the bi-metallic strip sits with its ends on an elastic bed.